1. Field of the Invention
The present invention relates to an optical integrated semiconductor light emitting device capable of emitting a plurality of light, particularly to an optical integrated semiconductor light emitting device such as a multibeam laser diode device which can be suitably applied to a high density optical disk unit and a laser beam printer.
2. Description of the Related Art
In these years, as a light source of a high density optical disk unit and a laser beam printer, the multibeam laser diode device capable of driving a plurality of beams independently has attracted attention. The laser device has, for example, a Group III-V nitride semiconductor layer, in which an n-type buffer layer, an n-type cladding layer, an n-type guide layer, an active layer, a p-type guide layer, a p-type cladding layer, and a p-type contact layer are layered in this order on the surface of a GaN (gallium nitride) substrate. In the upper section of the Group III-V nitride semiconductor layer, specifically in the upper section of the p-type cladding layer and the p-type contact layer, a plurality of stripe-shaped ridges are formed. Each light emitting region (current injection region) formed in the region opposed to the plurality of ridges is separated from each other by the groove between the ridges. Further, an individual electrode (p-side electrode) is formed on each ridge, and a common electrode (n-side electrode) is formed on the whole rear face of the GaN substrate. A pair of reflector films is formed on the end faces perpendicular to the extending direction of each ridge.
In the multibeam laser diode device with such a structure, when a voltage with a given potential difference is applied between the selected individual electrode and the common electrode, a current is confined by the ridge, the current is injected to the current injection region of the active layer, and thereby light is emitted by electron-hole recombination. The light is reflected by the pair of reflector films, laser oscillation is generated in the wavelength in which phase change when the light reciprocates once in the device becomes integral multiple of 2 π, and the light is emitted as a beam outside from one of the reflector films.
In general, the foregoing GaN substrate has a structure in which a plurality of high defect regions are irregularly formed through low defect regions. In particular, in the case of the multibeam laser diode device having a plurality of light emitting regions, it is inevitable that the light emitting regions are formed in the high defect regions, leading to lowering of light emitting characteristics and reliability of the device. Therefore, in order to solve such a disadvantage, a method in which a Group III-V nitride semiconductor layer is layered on a GaN substrate in which high defect regions are regularly (cyclically) arranged in low defect regions has been proposed (refer to Japanese Unexamined Patent Application Publication No. 2003-124572). Thereby, it becomes possible to surely form a plurality of light emitting regions in the low defect regions, and to improve light emitting characteristics and reliability of the device.